Most known lightning protection systems for wind turbine blades comprise one or more internally arranged down conductors and a number of lightning receptors arranged on the external surface of the blade. Typically, there is a tip receptor arranged at the tip of the wind turbine blade and a number of side receptors distributed on the surface of the wind turbine blade along at least a part of the length thereof.
It is a well-known problem that such external lightning receptors can be damaged by lightning impacts and that, therefore, the lifetime of such receptors is limited, depending on the number of lightning impacts to which they are subjected.
A typical side receptor as known in the art simply consists of a metal bolt, the head of which is aligned with the external surface of the wind turbine blade and the thread part of which is screwed into a side receptor base arranged within the wind turbine blade. The electrically conducting side receptor base is electrically grounded so that the current from lightning strikes impacting the head of the side receptor passes through the thread part thereof to the side receptor base and further through the wind turbine blade and the wind turbine tower to the ground.
A number of problems are related to the use of such typical side receptors. For instance, the head of the side receptor is often damaged by the impacts of lightning strikes. This means that any recesses (slots) or other structural elements in the head meant for engagement by tools may have at least partly disappeared after a number of lightning impacts. Therefore, it is often more or less impossible to unscrew the side receptor, for instance in order to replace it. Ironically, the more a replacement of a side receptor is needed, the more difficult it may be to remove it.
Another problem is that, because the lightning current must pass through the threads of the side receptor, manufacturers are often reluctant to use threadlockers or other adhesives for securing the side receptor because it may reduce the conductivity between the side receptor and the side receptor base.
Similar problems exist when it comes to replacement of tip receptors known in the art, especially when the tip receptors have been damaged by the impacts of lightning strikes.